Described below is a telecommunication system featuring a first network and a second network, and a method for controlling switching of a user terminal between the first network and the second network.
At present there is on ongoing expansion of cellular mobile radio networks, especially of the 3rd generation, i.e. primarily in accordance with what is known as the Universal Mobile Telecommunications System, UMTS standard. At the same time further radio networks are being developed which are aiming to provide subscribers with greater bandwidths, to enable large volumes of data to be transmitted in a short period. Such a radio network has been planned for some time now by a number of interested parties, who have joined together to form what is known as the WiMAX, Worldwide Interoperability for Microwave Access, Forum (www.wimaxforum.org) in order to create a standard for a WiMAX radio network. The intention is for user terminals, such as mobile telephones or notebooks for example, to have access to both conventional mobile radio networks such as the UMTS network, and also to the WiMAX radio network. This allows users to select the network most suitable for them according to specific criteria, such as availability, price, quality, etc., for example, and to switch as required between two different networks.
Data losses or interrupted connections can occur when switching between two networks, and such problems should be avoided. For this reason such a switch between two different networks is supported by a mobility protocol. The task of the mobility protocol is to maintain existing communication links of a user when switching networks and to avoid interruptions or at least to minimize them in such cases.
Such a mobility protocol has been defined for example by the WiMAX Forum above all on the basis of the so-called Mobile IP protocol, especially of the Mobile IP protocol Version 4, MIPv4, of the Internet Engineering Task Force, IETF. The WiMAX Forum has defined two different variants for using Mobile IP. One defines a Client Mobile IP, CMIP, client which is installed directly in the user terminal and handles the signaling for the switch between the two networks via the user terminal. Another defines a so-called Proxy Mobile IP, PMIP, client, which is installed in the network and represents a proxy for the user terminal in the network in respect of the switch between the networks. The PMIP handles the signaling for switching between the networks for the user terminal. In this case the user terminal is largely unaware that the mobility protocol is being used in the network.